Preparing all skin viscose rayon



2,926,099 PREPARING ALL SKIN VISCOSE RAYON Marion R. Lyt ton, West Chester, Pa., assignor to American Viscose Corporation, Philadelphia, Pa., a corporation of Delaware No Drawing. Application December 5, 1955 Serial No. 550,855

4 Claims. (Cl. 106-165) This invention relates to the production of shaped bodies of regenerated cellulose from viscose and more particularly to filaments and fibers of regenerated cellulose from viscose.

In the conventional methods of producing shaped bodies of regenerated cellulose from viscose, a suitable cellulosic material such as purified cotton linters, wood pulp, mixtures thereof, andthe like is first converted to an alkali cellulose by treatment with a caustic soda solution and after shredding the treated cellulose material,

it is allowed to age. The aged alkali cellulose is then converted to a xanthate by treatment with carbon disulfide. The cellulose xanthate is subsequently dissolved in a caustic soda solution in an amount calculated to provide a viscose of the desired cellulose and alkali content. After filtration, the viscose solution is allowed to ripen and is subsequently extruded through a shaped orifice into a suitable coagulating and regenerating bath.

In the production of shaped bodies such as filaments, the viscose solution is extruded through a spinneret into a coagulating and regenerating bath consisting of an aqueous acid solution containing zinc sulfate. The filament may subsequently be passed through a hot aqueous bath where it is stretched to improve its properties such as tensile strength. The filament may then be passed through a dilute aqueous solution of sulfuric acid and sodium sulfate to complete the regeneration of the cellulose, in case it is not completely regenerated upon leaving the stretching stage. The filament is subsequently subjected to washing, purification, bleaching, possibly other treating operations and drying, being collected either before or after these treatments.

The filaments as formed by the conventional methods, consist of a skin or outer shell portion and a core portion with a sharp line of demarkation between the two. The cross-section of the filaments exhibits a very irregular or crenulated exterior surface when even small amounts of zinc salts or certain other polyvalent metal salts are present in the spinning bath. The skin and core portions of the filament represent differences in structure and these diiferent portions possess different swelling and staining characteristics, the latter permitting a ready identification of skin and core. The sharply irregular and crenulated surface structure has a relatively low abrasion resistance and readily picks up foreign particles such as dirt. Although the core portion possesses a relatively high tensile strength, it has a low abrasion resistance and a low flex-life, is subject to fibrillation and is relatively stilt.

It has now been discovered that the presence of small amounts of certain alkali-soluble alkylene oxide adducts of l-m-hydroxyphenyl-8-p-hydroxyphenyl hexadecane in viscose results in the production of shaped bodies of regenerated cellulose such as filaments, films, sheets and the like composed of all skin and having improved properties and characteristics providing that the amount of the alkylene oxide adduct is maintained with certain limits and the composition of the spinning bath is maintained within certain composition limits which will be defined hereinafter. The most readily distinguishable characteristics as compared to conventional filaments include a smooth, non-crenulated surface and the filaments consist entirely of skin.

This invention contemplates the use of such compounds as are more technically classed as polyoxyalkylene glycol ethers of 1-m-hydroxyphenyl-8-p-hydroxyphenyl hexadecane; for example, the ethers of ethylene, and propylene having at least 30 to about 100 or more alkylene oxide units per molecule, preferably between about 35 to about alkylene oxide units per molecule. It is possible that the adducts or ethers may have hydroxy polyoxyalkylene chains of different lengths and that the alkylene oxide units are not in all cases equally distributed at the two phenyl radicals. The alkylene oxide content of the ethers may be conveniently expressed as the average num ber of alkylene oxide units per molecule of the l-m-hydroxyphenyl-8-hydroxyphenyl hexadecane. The ethers in all cases must have sufficient water and alkali solubility to permit the required amount to be dissolved in the viscose. It is obvious that for all practical purposes considering cost, ease of preparation, commercial availability and solubility in water and in alkali solutions, the ethylene oxide adducts or polyoxyethylene glycol ethers are preferred. For purposes of illustration only, the invention is described by reference to the ethylene oxide adducts but it is to be understood that other alkylene oxide adducts such as propylene oxide adducts are equally satisfactory so long as they possess the required solubility. The production of all skin products requires that certain minimum and limited amounts of the ether be in solution in the viscose. The ether may be conveniently added to the viscose in the form of a solution in alkali or in Water.

The amount of the ether. or adduct which is incorporated in the viscose must be at least about 0.75% by weight of the cellulose in the viscose and may vary up to about 3%, preferably, the amount varies from 1% to 2.5%. Lesser amounts do not result in the production of products consisting entirety of skin and greater amounts alfect adversely the physical properties of the products. Amounts Within the preferred range are most effective in enhancing the characteristics and properties of the products. The ether or adduct may be added at any desired stage in the production of the viscose such as in the preparation of the refined wood pulp for the manufacture of viscose, before or during the shredding of the alkali cellulose, to the xanthated cellulose while it is being dissolved in the caustic solution or to the viscose solution before or after filtration. The adduct .is preferably added after the cellulose xanthate has been dissolved in the caustic solution and prior to filtration.

The viscose may contain from about 4% to about 10% cellulose, the particular source of the cellulose being selected for the ultimate use of the regenerated cellulose product. The caustic soda content may be from about 4% to about 8% and the carbon disulfide content may be from about 30% to about 50% based upon the weight of the cellulose. The modified viscose, that is, a viscose containing the small amount of an alkylene oxide adduct as described may have a sodium chloride salt test above about 8 and preferably above about 9 at the time of spinning or extrusion.

In order to obtain the improvements enumerated hereinbefore, it is essential that the composition of the spinning bath be maintained Within a Well defined range. The presence of the ether or adduct in the viscose combined with these limited spinning baths results in the production of yarns of improved properties such as high tenacity, high abrasion resistance, high fatigue resistance and consisting of filaments composed entirely of skin.

Generically and in terms of the industrial art, the spinning bath is a low acid-high zinc spinning bath containing from about 10% to about 25% sodium sulfate and from about 3% to about 15% zinc sulfate, preferably from 15 to 22% sodium sulfate and from 4% to 9% zinc sulfate. Other metal sulfates such as iron, manganese, nickel and the like may be present and may replace some of the zinc sulfate. The temperature of the spinning bath may vary from about 25 C. to about 80 0, preferably between about 45 C. and about 70 C. In the production of the all skin type filaments, the temperature of the spinning bath is not critical, however, as is well known in the conventional practice in the art, certain of the physical properties such as tensile strength vary directly with the temperature of the spinning bath. Thus, in the production of filaments for tire cord purposes in accordance with the method of this invention, the spinning bath is preferably maintained at a temperature between about 55 C. and 65 C. so as to obtain the desired high tensile strength.

The acid content of the spinning bath is balanced against the composition of the viscose. The lower limit of the acid concentration, as is well known in the art, is just above the slubbing point, that is, the concentration at which small slubs of uncoagulated viscose appear in the strand as it leaves the spinning bath. For commercial operations, the acid concentration of the spinning bath is generally maintained about 0.4% to 0.5% above the slubbing point. For any specific viscose composition, the acid concentration of the spinning bath must be maintained above the slubbing point and below the point at which the neutralization of the caustic of the viscose is sufficiently rapid to form a filament having a skin and core.

There is a maximum acid concentration for any specific viscose composition beyond which the neutralization is sufficiently rapid to produce filaments having a skin and core. For example, in general, the acid concentration of the spinning baths which are satisfactory for the production of the all skin products from a 7% cellulose, 6% caustic-viscose and containing the alkylene oxide adducts lies between about and about 8%. The acid concentration may be increased as the amount of the derivative is increased and also as the salt test of the viscose is increased. There is an upper limit, however, for the acid concentration based upon the amount of adduct and the concentration of caustic in the .viscose. All skin products cannot be obtained if the acid concentration is increased above the maximum value although the amount of the ether is increased beyond about 3% while other conditions are maintained constant.

Lesser amounts of sulfuric acid may be employed. Greater amounts of sulfuric acid result in the production of products having skin and core. A lowering of the amount of the ether, the lowering of the caustic soda content or the lowering of the salt test of the viscose reduces the maximum permissible acid concentration for the production of all skin filaments. It has been determined that the maximum concentration of acid which is permissible for the production of all skin products in accordance with the invention is about 9%.

The presence of the ethers or adducts in the viscose retards the coagulation and, therefore, the amount of adduct employed must be reduced at high spinning speeds. Thus, for optimum physical characteristics of an all skin yarn formed from a viscose as above and at a spinning speed of about 50 meters per minute, the adduct is employed in amounts within the lower portion of the range, for example, about 1%. The determination of the specific maximum and optimum concentration of acid for any specific viscose, spinning bath and spinning speed is a matter of simple experimentation for those skilled in the art. The extruded viscose must, of course, be immersed or maintained in the spinning bath for a period sufficient to effect relatively complete coagulation of the viscose, that is, the coagulation must be sufficient so that the filaments will not adhere to each other as they are brought together and withdrawn from the bath.

In the production of filaments for such purposes as the fabrication of tire cord, the filaments are preferably stretched after removal from the initial coagulating and regenerating bath. From the initial spinning bath, the filaments may be passed through a hot aqueous bath which may consist of hot water or a dilute acid solution and may be stretched from about 70% to about 120%, preferably between 75% and Yarns for other textile purposes may be stretched as low as 20%. The precise amount of stretching will be dependent upon the desired tenacity and other properties and the specific type of product being produced. If desired, the filaments may be stretched in air. It is to be understood that the invention is not restricted to the production of filaments and yarns but it is also applicable to other shaped bodies such as sheets, films, tubes and the like. The filaments may then be passed through a final regenerating bath which may contain from about 1% to about 5% sulfuric acid and from about 1% to about 5% sodium sulfate with or without small amounts of Zinc sulfate if regeneration has not previously been completed.

The treatment following the final regenerating bath, or the stretching operation where regeneration has been completed, may consist of a washing step, a desulfurizing step, the application of a finishing or plasticizing material and drying before or after collecting, or may include other desired and conventional steps such as bleaching and the like. The treatment after regeneration will be dictated by the specific type of shaped body and the proposed use thereof.

Regenerated cellulose filaments prepared from viscose containing the small amounts of the alkylene oxide adducts or polyoxyalkylene glycol ethers and spun in the spinning baths of limited acid content have a smooth or non-crenulated surface and consist substantially entirely of skin. Because of the uniformity of structure throughout the filament, the swelling and staining characteristics are uniform throughout the cross-section of the filament. Filaments produced pursuant to this invention and consisting entirely of skin have a high toughness and a greater flexing life than filaments as produced according to prior methods which may be attributed by the uniformity in skin structure throughout the filament. Although the twisting of conventional filaments, as in the production of tire cord, results in an appreciable loss of tensile strength, there is appreciably less loss in tensile strength in the production of twisted cords from the filaments consisting entirely of skin. Filaments prepared from viscose containing the alkylene oxide adducts have a high tensile strength as compared to normal regenerated cellulose filaments, have superior abrasion and fatigue resistance characteristics and have a high flexlife. Such filaments are highly satisfactory for the production of cords for the reinforcement of rubber products such as pneumatic tire casings, but the filaments are not restricted to such uses and may be used for other textile applications.

The invention may be illustrated by reference to the preparation of regenerated cellulose filaments from a viscose containing about 7.4% cellulose, about 6.6% caustic soda, and having a total carbon disulfide content of about 36% based on the weight of the cellulose. The viscose solutions were prepared by xanthating alkali cellulose by the introduction of 36% carbon disulfide based on the weight of the cellulose and churning for about 2 /2 hours. The cellulose xanthate was then dissolved in caustic soda solution. The viscose was then allowed to ripen for about 28 hours at 18 C. In those instances where an ethylene oxide adduct was incorporated in the viscose, the desired amount of an adduct or ether of the type described hereinbefore containing an average of 40 ethylene oxide units per molecule of the hexadecane derivative was added to the viscose solution and mixed for about hour before allowing the viscose to ripen.

In each instance, the viscose was extruded through a spinneret to form a 203 to 208 denier, 100 filament yarn at the rate set forth in the table which follows. The coagulating and regenerating bath was maintained at a temperature of about 60 C. The yarn after removal from the spinning bath was passed through a hot water bath maintained at about 95 C. and was stretched while passing through this bath. The yarn was collected in a spinning box, washed free of acid and salts and dried.

The specific spinning conditions and the physical properties of the yarns are set forth in the following table:

Example I II III IV V VI Viscose:

Percent Ether 1 2 0 1 2 0 lialt T st 9.2 9.4 8. 8 8.8 8.8 8.8 Percent H2804 7. 8 7. 8 7. 8 8.7 8. 7 8. 7 Percent ZHSO4 6 6 6 7 7 7 Percent N3zSO4 17 17 17 18 18 18 Spin (1 22 22 22 36 36 36 Percent Stretch 82 82 82 76 76 76 T. dry 3.2 3.2 3.0 2.9 2.4 2.9 T. Wet---" 2. 4 2. 6 2.3 2.0 1.4 2.0 E. dry... 20 20 19 18 16 18 E. wet 25 26 23 24 21 22 Percent Skin 100 100 60 100 100 60 Norm-Spin speed-Speed of extrusion of viscose in meters per minute. T. dry and T. wetTensile strength of dry and wet yarn, respectively, in grams per denier. E. dry and E. wet-Percent elongation of dry and wet yarn, respectively.

The individual filaments formed in accordance with this invention have a smooth, non-crenulated exterior surface and consist entirely of skin, no core being detectable at high magnification (e.g. l500x). The filaments of the control yarns (Examples III and VI) formed from the same viscose solution but without the addition of the modified agent and spun under the same conditions, exhibit a very irregular and serrated surface and are composed of about 60% skin and the balance core with a sharp line of demarkation between the skin and core.

Although the tenacity and elongation are the only properties set forth, they have been chosen because of the ease and simplicity with which such properties may be determined. In some instances, products made in accordance with this invention do not exhibit improvements in tenacity and elongation, however, the products consist of a smooth-surface, all skin structure and possess improved abrasion resistance, flex-life and other properties as disclosed hereinbefore.

One of the properties of viscose rayon which has limited its uses is its relatively high cross-sectional swelling when wet with water, this swelling amounting to from about 65% to about 80% for rayon produced by conventional methods. Rayon filaments produced in accordance with the method of this invention have an appreciably lower cross-sectional swelling characteristic, the swelling amounting to from about 45% to about 60%.

If desired, small amounts of the ether may be added to the spinning bath. Since the ethers are water-soluble, some of the ether will be leached from the filament or other shaped body and will be present in the bath.

The alkylene oxide others may be added to any desired viscose such as those normally used in industry, the specific viscose composition set forth above, being merely for illustrative purposes. The ethers may be added at any desired stage in the production of the viscose and may be present in the cellulosic raw material a1- though it may be necessary to adjust the amount present to produce a viscose having the proper proportions of the adduct at the time of spinning.

The term skin is employed to designate that portion of regenerated cellulose filaments which is permanently stained or dyed by the following procedure. A microtome section of one or more of the filaments mounted in a wax block is taken and mounted on a slide with Meyers albumin fixative. After dewaxing in xylene, the section is placed in successive baths of 60% and 30% alcohol for a few moments each, and it is then stained in 2% aqueous solution of Victoria Blue BS conc. (General Dyestuifs Corp.) for 1 to 2 hours. At this point, the entire section is blue. By rinsing the section first in distilled water and then in one or more baths composed of 10% water and dioxane for a period varying from 5 to 30 minutes depending on the particular filaments, the dye is entirely removed from the core, leaving it restricted to the skin areas.

While preferred embodiments of the invention have been disclosed, the description is intended to be illustrative and it is'to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined by the appended claims.

I claim:

1. A viscose spinning solution containing a small amount of alkali-soluble polyoxyalkylene glycol ether of 1 m hydroxyphenyl-8-p-hydroxyphenyl hexadecane wherein the alkylene oxide is selected from the group consisting of ethylene oxide and propylene oxide and the ether contains at least 30 to about alkylene oxide units per molecule, said small amount of the modifier being a quantity sufiicient to impart a smooth, noncrenulated surface and a substantially all skin structure to products formed by spinning the viscose at a salt test of at least 8 into an aqueous bath containing from 10% to 25% sodium sulfate, from 3% to 15% zinc sulfate and sulfuric acid in a percentage not exceeding 9%, but the quantity being insufficient to adversely affect the physical properties of such products.

2. A viscose spinning solution as defined in claim 1 wherein the ether is a polyoxyalkylene glycol ether containing between about 35 and about 80 ethylene oxide units per molecule.

3. A viscose spinning solution containing from about 4% to about 10% cellulose and from about 0.75% to about 3%, based on the weight of the cellulose in the viscose, of an alkali-soluble polyoxyalkylene glycol ether of 1 m hydroxyphenyl-8 p-hydroxyphenyl hexadecane wherein the alkylene oxide is selected from the group consisting of ethylene oxide and propylene oxide and the ether contains at least 30 to about 100 alkylene oxide units per molecule.

4. A viscose spinning solution as defined in claim 3 wherein the ether is a polyoxyalkylene glycol ether containing between about 35 and about 80 ethylene oxide units per molecule.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A VISCOSE SPINNING SOLUTION CONTAINING A SMALL AMOUNT OF ALKALI-SOLUBLE POLYOXYALKYLENE GLYCOL ETHER OF 1-M-HYDROXYPHENYL-8-P-HYDROXYPHENYL HEXADECANE WHEREIN THE ALKYLENE OXIDE IS SELECTED FROM THE GROUP CONSISTING OF ETHYLENE OXIDE AND PROPYLENE OXIDE AND THE ETHER CONTAINS AT LEAST 30 TO ABOUT 100 ALKYLENE OXIDE UNITS PER MOLECULE, SAID SMALL AMOUNT OF THE MODIFIER BEING A QUANTITY SUFFICIENT TO IMPART A SMOOTH, NONCRENULATED SURFACE AND A SUBSTANTIALLY ALL SKIN STRUCTURE TO PRODUCTS FORMED BY SPINNING THE VISCOSE AT A SALT TEST OF AT LEAST 8 INTO AN AQUEOUS BATH CONTAINING FROM 10% TO 25% SODIUM SULFATE, FROM 3% TO 15% ZINC SULFATE AND SULFURIC ACID IN A PERCENTAGE NOT EXCEEDING 9%, BUT THE QUANTITY BEING INSUFFICIENT TO ADVERSELY AFFECT THE PHYSICAL PROPERTIES OF SUCH PRODUCTS. 